The Center for Science in the Public Interest (CSPI), a consumer interest group, released a report today linking Coca-Cola, Diet Coke, Pepsi and Diet Pepsi -- the 1st-, 2nd-, 3rd- and 6th- best-selling sodas in the world, respectively -- to a chemical that has been known to cause cancer in lab rats and mice. The report has raised alarm bells, not for the first time, about the risks soda poses to public health -- even though many experts were quick and unequivocal in their denunciation of its findings.

The chemical, 4-methylimidazole, usually known as 4-MI and sometimes 4-MEI, is a byproduct of the chemical process soda companies use to create the artificial dye that gives the sodas their trademark caramel coloring. Studies linking 4-MI to cancer in mice prompted the state of California to list it as a carcinogen in spring of 2009. It's illegal to sell any food or beverage containing an amount of 4-MI that could increase the risk of cancer by more than 1 case per 100,000 people in California without a warning label. The CSPI alleges that the levels it found in sodas would increase the risk by as much as 4.8 cases per 100,000 people.

"Time and again, and even very recently," the ABA wrote in its statement on the report, "leading public health organizations have reaffirmed that caramel coloring, including the trace amounts of 4-MEI found in it, is safe for use in colas and countless other foods."

A Vanderbilt University biochemist told Time's Bryan Walsh that 4-MI would only increase a person's risk of cancer if he or drank 1000 cans of cola per day.

And this also isn't the first time the CSPI has tried to raise awareness about what it perceives as the risks of 4-MI. It did so in a report and petition last February as well. That release did not, however, include test results for individual brands of soda.

UPDATE 3/7: NPR reported today that Coca-Cola is tweaking the recipe it uses to make the caramel dye that it uses to color its product to reduce the chance that its soda cans would get a warning label in California. But Coca-Cola spokesperson Ben Sheidler affirmed the safety of the company's product in an email to the Huffington Post. "The 4-MEI levels in our products pose no health or safety risks," he said. "Outside of California, no regulatory agency concerned with protecting the public's health has stated that 4-MEI is a human carcinogen. The caramel color in all of our ingredients has been, is and always will be safe."

UPDATE 3/8: The AP now reports that Pepsi is also rejiggering its dye formula to avoid a warning label in California. Both Pepsi and Coca-Cola, the AP continues, have plans to take the new formula national at some point in the future.